1. Field of the Invention
The present invention relates to an optical recording and reproducing apparatus, which is particularly suitable for recording/reproducing information on/from a write-once-read-many (hereinafter, referred to as WORM) optical disk.
2. Description of the Related Art
Recording media (optical disks) currently in use are classified into three major types as follows: a read only type medium such as a CD-ROM or a DVD-ROM; a rewritable type medium such as a CD-RW or a DVD-RW; and a WORM medium such as a CD-R, a DVD-R, or a DVD+R. Although WORM media such as a CD-R, a DVD-R, and a DVD+R can each be recorded only one time, those media are popular as they are cheap in comparison with rewritable type media and also maintain high compatibility with read only type media such as a CD-ROM and a DVD-ROM.
A WORM medium has a power calibration area (PCA) for adjusting laser power, and normal recording/reproducing operation is performed after laser power is adjusted using the PCA. In this case, however, it is impossible to adjust laser power after the PCA is used up, then recording operation is not usually performed after the PCA is used up.
As described above, the recordable capacity of the conventional WORM media is significantly influenced by the usage state of its PCA. When recording onto the disk is performed frequently and therefore the usage frequency of the PCA increases, there occurs a situation where further recording onto the disk becomes impossible even though a large free capacity remains on the disk. This inconvenient situation will become a more serious problem with further increases in capacities of such WORM media in the future.
JP 2002-175624 A discloses a technique in which a laser power adjustment area (outer power calibration area) is provided in an outermost circumference portion of a WORM medium as well as an innermost circumference portion of it and the laser power is appropriately adjusted using the adjustment area as required. According to this technique, adjustment of laser power using the outer power calibration area other than ordinary PCA can be performed, whereby the medium usability is improved when compared with the above-mentioned cases.
However, even in the advancing technique, there also arises a problem in that recording operation is not performed after the outer power calibration area is used up as with the above-mentioned case, and therefore media usability reduces.
In addition, the WORM disk varies in recording sensitivity within its recording surface. When laser power adjustment is performed using the outer power calibration area, laser power may not be adjusted to an appropriate value. The recording layer of the disk is formed through application using a spin coat method in ordinary cases, so the characteristics of the recording layer change abruptly as a distance to an outer peripheral portion of the disk is reduced. Therefore, when laser power adjustment with respect to a recording position in an inner peripheral portion or a central portion of the disk is performed using the outer power calibration area, laser power determined through the laser power adjustment may greatly depart from an originally appropriate value.